1. Field of the Invention
The present invention relates to an ornamental part utilized in watchcases, watchbands, spectacle frames, accessories and the like.
2. Description of the Prior Art
Conventionally, gold or gold alloy material or gold-plated material has been utilized as gold colored ornamental parts. Recently, studies on physical vapor deposition processes have advanced, and super-hard compound coatings with very high wear-resistance, compounds such as gold colored titanium nitride, zirconium nitride, and tantalum nitride, have been developed, and are beginning to be widely used as ornamental parts. Also, as a gold external portion combining the characteristics of titanium nitride coatings and of gold plating, a gold colored ornamental part constructed of titanium nitride coating as the foundation layer and of gold or gold alloy coating on the upper part are being made. For example, ornamental parts of this type are disclosed under Japanese Provisional Publication No. 139037/1975 and Japanese Patent Publication No. 26664/1984.
Utilizing pure gold material or gold plating in the conventional way is expensive from the standpoint of material cost, and has some drawbacks such as in wear-resistance and corrosion-resistance, and also requires a certain thickness of the plating (more than 10 .mu.m). Also, when utilizing titanium nitride coating, there are drawbacks in that the color is darker than gold, and that its quality is inferior. Although coatings other than titanium nitride, such as zirconium nitride and tantalum nitride, do have a gold color with better quality compared to titanium nitride, the color is still inferior to the color of gold. Furthermore, in forming these coatings, the deposition rate compared to that of the titanium nitride is very slow, there being a necessity for a long process time to obtain a coating with similar efficiency, and so as a result, the yield becomes low, the cost becomes high, and thus such coating are difficult to realize commercially. With a titanium nitride coating on which gold or gold alloy film is formed, when the gold or gold alloy layer becomes worn, the titanium nitride layer at the lower layer appears, and presents an unpleasant appearance because of its dark color which is noticeably different from the gold color.